Chemical mechanical polishing (CMP) is currently a new planarization technology employed in the manufacturing process of large scale integrated circuits as well as very large scale integrated circuits. In a CMP process, slurry is used as a medium and a wafer is pressed against a polishing pad so that the surface of the wafer is polished by the method of rotational polish on the polishing pad. The parameters that affect the CMP process are: the composition of the slurry, the polishing pressure on the wafer, the wafer rotating speed during polishing, the material of the polishing pad, the size distribution of the abrasive in the slurry, the feed rate of slurry, and the working temperature, etc. Among these parameters, the polishing pressure on the wafer is the subject matter of the following description.
Referring to FIG. 1, a conventional CMP apparatus includes: a wafer 11 to be treated; a polishing pad 12; a distribution pad 13; a carrier head 14 for gripping the wafer 11; a carrier quick connector 15 for quickly connecting/disconnecting the carrier head 14 and the components (not shown) that drive the carrier head 14; a protection rubber 16 for protecting the above-mentioned components from being directly splashed by the slurry; and a slurry nozzle 17 for supplying the slurry required in CMP.
Referring to FIG. 2, the slurry nozzle 17 includes six slurry lines 171 and a slurry nozzle enclosure 172 for enclosing the six slurry lines 171 so as to provide six different types of slurry used in various conditions.
Referring to FIG. 3, the CMP apparatus is provided with five carrier heads 14 that deal with five wafers at one time. The slurry nozzle 17 is above the center of the polishing pad 12 and the five carrier heads 14 are arranged in a radial pattern from the center of the polishing pad 12. After the slurry is dispersed downward from the slurry nozzle 17 (in a direction perpendicular to the figure), it falls into the distribution pad 13. The distribution pad 13 is mounted onto the polishing pad 12 and is rotated simultaneously with it (the rotation direction is noted by an arrow) to distribute the slurry to the region around the polishing pad 12. The carrier head 14 is used to grip and rotate the wafer 11 in a direction shown by the arrow. By means of the rotation of wafer 11 and the polishing pad 12, together with the slurry, the wafer 11 is thus polished.
Some drawbacks of the above-mentioned CMP apparatus will be described in the following.
In a normal situation, the slurry flows in a specific flow rate so as to facilitate the planarization process. In order to provide a larger flow rate, the flow speed and the pressure of the slurry in the slurry lines 171 have to be increased. Thus, in the polishing process, the slurry impinges onto the distribution pad 13 with a large speed and this causes the slurry to splash and adhere onto the carrier head 14, the carrier quick connector 15, and the protection rubber 16 (referring to the arrow as shown in FIG. 1). After the slurry dries, the dried slurry can strip and fall onto the polishing pad 12. If this occurs in the polishing process, the wafer 11 can be easily damaged.
In addition, if too much slurry is adhered to the carrier head 14, the carrier quick connector 15, and the protection rubber 16, the polishing pressure exerted to the wafer increases, and affects both the uniformity and the removing rate of the wafer.
Furthermore, the splashed slurry adhered to the carrier head 14 becomes a waste of material. Besides, the dried slurry adhered to the carrier head 14, the carrier quick connector 15, and the protection rubber 16 causes a difficulty to maintain the apparatus.